The Drill Enrichment Behavior Study

Problems:

1. Does the enrichment given to the male drill affect the amount of positive and negative mating behaviors?
2. Does dominance play a role in the amount of time a female will spend with the enrichment item given on an enrichment day?

Subjects

Eschu

Nora

Bioko

Lyle

Hypotheses:

Hypothesis 1:
Does the male drill exhibit more negative mating behaviors on enrichment, than on non-enrichment days?

Hypothesis 2:
Does the male drill exhibit more positive mating behaviors on non-enrichment days than on enrichment days?

Hypothesis 3:
Is the mean of the time the dominant female spend with the enrichment greater than the mean of the time the non-dominant female spends with the enrichment?

Statistical Test:

The statistical test used is a z-test of independent sample means. The z-test will be run for the means of the number of time the male drill exhibited a negative mating behavior on enrichment days and non-enrichment days, the number of time the male drill exhibits positive mating behaviors on enrichment days and non-enrichment days, and the mean of the activity time with the enrichment items from Eschi and Nora. The confidence level for the study was 95%.

Abstract:

The hypotheses of this study were: does the male drill exhibit more negative mating behaviors on non-enrichment days than on enrichment days, does the male drill exhibit more positive mating behaviors on enrichment days than on non-enrichment days, and is the mean of the time the dominant female spends with the enrichment greater than the mean of the time the non-dominant female spends with the enrichment. The data was collected over a total of 76 days. These days were split into 33 enrichment days and 43 non-enrichment days. Each day the observer would collect data on the drills over a period of 2 hours. The subjects studied were: Eschu, Nora, Bioko, and Lyle. Data collected were: the total time the observer watched in minutes, the time active in minutes, the time inactive in minutes, the time insight in minutes, the time out of sight in minutes, the time spent with enrichment in minutes, the number of negative mating behaviors shown by the male drill, the number of positive mating behaviors shown by the male drill, the time in seconds that the male drill self aggressed, what enrichment was given on the enrichment day, and a rating for how well the drills liked that item. The data collected that was used in this study was the time spent with enrichment in minutes by the two youngest and more dominate females (Eschu and Nora), the number of negative mating behaviors shown by the male drill, and the number of positive mating behaviors shown by the male drill. The tests were all ran on z-tests at an alpha level of .95. Each test was unable to reject its null showing that there was not enough data to support the claim. This means that the study was inconclusive.

Movies:

Procedure

Conclusion

Results:

The purpose of this study was to determine if enrichment has an effect on the mating behaviors of the male drill, and if dominance affects the activity level of the female drills in the amount of time they spend with the enrichment. It was hypothesized that the enrichment would cause the male to exhibit more positive mating behaviors on enrichment days and that the more dominate female will be more active with the enrichment than the non-dominate female. The chapter presents information on the tests run and the results of those tests.

Table 1. Descriptive Statistics of the Male Drill’s Negative Mating Behaviors

  Negative Mating Behaviors on Enrichment Days Negative Mating Behaviors for Non-Enrichment Days
Observations 33 days  43 days
Mean 1.21 negative mating behaviors per enrichment day 0.58 negative mating behaviors per non-enrichment day
Standard Dev. 2.655 1.118
Variance 7.047 1.249
Confidence Interval for Means
 (0.31, 2.12) (0.25, 0.92)
Confidence Interval for Variance (5.152, 12.195) (0.941, 1.979)
df 32 42

In Table 1 the descriptive statistics of the male drill’s positive mating behaviors were shown. Table 1 also includes confidence intervals for both the mean and the variance. The n for the samples are 33 and 43 respectively; this means the data were gathered over 33 enrichment days and 43 non-enrichment days. The mean for the negative mating behaviors on enrichment days is 1.21 negative mating behaviors per enrichment day. The mean for the negative mating behaviors on non-enrichment days is 0.58 negative mating behaviors per non-enrichment day. The mean for each set of data falls within its confidence interval. The confidence interval for the mean for the enrichment days for negative mating behaviors is (0.31, 2.12). The confidence interval for the mean for the non-enrichment days for negative mating behaviors is (0.25, 0.92). The variance for negative mating behaviors on enrichment days is 7.047. The variance for the negative mating behaviors on non-enrichment days is 1.249. The variance for each set falls within its confidence interval. The confidence interval for the variance for the enrichment days for negative mating behaviors is (5.152, 12.195). The confidence interval for the variance for the non-enrichment days for negative mating behaviors is (0.941, 1.979).

Table 2. Results of z-Test: Two Sample for Means for the Male Drill’s Negative Mating Behaviors

  Enrichment Days Non-Enrichment Days
Mean 1.21 negative mating behaviors per enrichment day 0.58 negative mating behaviors per non-enrichment day
Variance 7.047 1.118
Observations 33 days 43 days
Hypothesized Mean Difference 0  
z Stat 0.69  
Critical z 1.64 Fail to Reject

Table 2 contains the results of the z-test for the two sample means for the male drill’s negative mating behaviors. The mean for the negative mating behaviors on enrichment days is 1.21 negative mating behaviors per enrichment day. The mean for the negative mating behaviors on non-enrichment days is 0.58 negative mating behaviors per non-enrichment day. The hypothesized difference in means is 0. That means that if the z stat is rejected the means will be significantly different. The z statistic was 0.69. The critical z was 1.64. The z stat is not larger than the critical z. This means that the null could not be rejected showing that there is not enough evidence to support the claim that Lyle will exhibit more negative mating behaviors on non-enrichment days than on enrichment days.


Figure 5. Mean Comparison of Lyle’s Negative Mating Behaviors on Enrichment Days and Non-Enrichment Days

Figure 5 is a visual of a mean comparison between Lyle’s negative mating behaviors on enrichment and non-enrichment days. This shows that the means of Lyle’s negative mating behaviors on enrichment days is slightly larger than the mean of Lyle’s negative mating behaviors on non-enrichment days.

Table 3. Results of f-Test: Two Sample for Variance for the Male Drill’s Negative Mating Behaviors

  Non-Enrichment Days Enrichment Days
Mean 1.21 negative mating behaviors per non-enrichment day 0.58 negative mating behaviors per enrichment day
Variance 7.047 1.249
Observations 43 days 33 days
df 42 32
f Stat 5.642  
Critical f 1.88 Reject

Table 3 contains the results of the f-test for the two sample variance for the male drill’s negative mating behaviors. The variance for negative mating behaviors on enrichment days is 7.047. The variance for the negative mating behaviors on non-enrichment days is 1.249. The degrees of freedom are 42 for the non-enrichment days and 32 for the enrichment days. If the f statistic is rejects the null the variances will be significantly different. The f statistic was 5.642. The critical f was 1.88. The f statistic is larger than the critical f. This means that the null could be rejected showing that variances are significantly different.


Figure 6. Variance Comparison of Lyle’s Negative Mating Behaviors on Enrichment Days and Non-Enrichment days.

Figure 6 is a visual of a variance comparison between Lyle’s negative mating behaviors on enrichment and non-enrichment days. This shows that the variance of Lyle’s negative mating behaviors on enrichment days is significantly larger than the variance of Lyle’s negative mating behaviors on non-enrichment days. The large difference in the variances shows that the range of the data is one is significantly greater than in the other.


Table 4. Descriptive Statistics of the Male Drill’s Positive Mating Behaviors

  Positive Mating Behaviors on Enrichment Days Positive Mating Behaviors for Non-Enrichment Days
Observations 33 days  43 days
Mean 0.24 positivemating behaviors per enrichment day 0.14 positive mating behaviors per non-enrichment day
Standard Dev. 0.751 0.467
Variance 0.564 0.218
Confidence Interval for Means
 (-0.01, 0.50) (0.00, 0.28)
Confidence Interval for Variance (0.324, 0.681) (0.209, 0.495)
df 32 42

In Table 4 the descriptive statistics of the male drill’s positive mating behaviors were shown. Table 4 also includes confidence intervals for both the mean and the variance. The n for the above data is 33 and 43 respectively; this means the data were gathered over 33 enrichment days and 43 non-enrichment days. The mean for the positive mating behaviors on enrichment days is 0.24 positive mating behaviors per enrichment day. The mean for the positive mating behaviors on non-enrichment days is 0.14 positive mating behaviors per non-enrichment day. The mean for each set of data falls within its confidence interval. The confidence interval for the mean for the enrichment days for positive mating behaviors is (-0.01, 0.50). The confidence interval for the mean for the non-enrichment days for positive mating behaviors is (0.00, 0.28). The variance for positive mating behaviors on enrichment days is 0.564. The variance for the positive mating behaviors on non-enrichment days is 0.218. The variance for each set falls within its confidence interval. The confidence interval for the variance for the enrichment days for positive mating behaviors is (0.324, 0.681). The confidence interval for the variance for the non-enrichment days for positive mating behaviors is (0.209, 0.495).

Table 5. Results of z-Test: Two Sample Means for the Male Drill’s Positive Mating Behaviors

  Enrichment Days Non-Enrichment Days
Mean 0.24 positive mating behaviors per enrichment day 0.14 positve mating behaviors per non-enrichment day
Variance 0.564 0.218
Observations 33 days 43 days
Hypothesized Mean Difference 0  
z Stat 1.28  
Critical z 1.64 Fail to Reject

Table 5 contains the results of the z-test for the two sample means for the male drill’s positive mating behaviors. The mean for the positive mating behaviors on enrichment days is 0.24 positive mating behaviors per enrichment day. The mean for the positive mating behaviors on non-enrichment days is 0.14 positive mating behaviors per non-enrichment days. The hypothesized difference in means is 0. That means that if the z stat is rejected the means will be significantly different. The z statisitic was1.28. The critical z was 1.64. The z statistic is not larger than the critical z. This means that the null could not be rejected showing that there is not enough evidence to support the claim that Lyle will exhibit more positive mating behaviors on enrichment days than on non-enrichment days.

Figure 7. Mean Comparison of Lyle’s Positive Mating Behaviors on Enrichment Days and Non-Enrichment Days

Figure 7 is a visual of a mean comparison between Lyle’s positive mating behaviors on enrichment and non-enrichment days. This shows that the means of Lyle’s positive mating behaviors on enrichment days is slightly larger than the mean of Lyle’s positive mating behaviors on non-enrichment days.

Table 6. Results of f-Test: Two Sample for Variance for the Male Drill’s Positive Mating Behaviors

  Enrichment Days Non-Enrichment Days
Mean 0.24 negative mating behaviors per enrichment day 0.58 negative mating behaviors per non-enrichment day
Variance 0.564 0.218
Observations 33 days 43 days
df 32 42
f Stat 0.387  
Critical f 1.822 Fail to Reject

Table 6 contains the results of the f-test for the two sample variance for the male drill’s positive mating behaviors. The variance for positive mating behaviors on enrichment days is 0.564. The variance for the positive mating behaviors on non-enrichment days is 0.218. The degrees of freedom are 42 for the non-enrichment days and 32 for the enrichment days. If the f statistic is rejects the null the variances will be significantly different. The f stat was 0.387. The critical f was 1.822. The f stat is larger than the critical f. This means that the null could be not rejected showing that variances are equal.

Figure 8. Variance Comparison of Lyle’s Positive Mating Behaviors on Enrichment Days and Non-Enrichment Days.

Figure 8 is a visual of a variance comparison between Lyle’s positive mating behaviors on enrichment and non-enrichment days. This shows that the means of Lyle’s positive mating behaviors on non-enrichment days is slightly larger than the mean of Lyle’s positive mating behaviors on enrichment days. The two variances are equal, this shows that the range in the number in the two data sets are very close.

Table 7. Descriptive Statistics of the Female Drills’ Activity Time with Enrichment

  Eschu Nora
Observations 33 days  33 days
Mean 412 minutes 373 minutes
Standard Dev. 21.173 23.285
Variance 448.313 542.171
Confidence Interval for Means
 (404, 419) (365, 381)
Confidence Interval for Variance (327.736, 775.754) (396.351, 938.164)
df 32 32

In Table 7 the descriptive statistics of the female drill’s activity time with enrichment is shown. Table 7 also includes confidence intervals for both the mean and the variance. The n for the above data is 33; this means the data were gathered over 33 enrichment days. The mean for Eschu the non-dominant female is 412 minutes. The mean for Nora the dominant female is 373 minutes. The mean for each set of data falls within its confidence interval. The confidence interval for the mean for Eschu the non-dominant female is (404, 419). The confidence interval for the mean for Nora the dominant female is (365, 381). The variance for positive mating behaviors on enrichment days is 448.313. The variance for the positive mating behaviors on non-enrichment days is 542.171. The variance for each set falls within its confidence interval. The confidence interval for the variance for Eschu the non-dominant female is (327.736, 775.754). The confidence interval for the variance for Nora the dominant female is (396.351, 938.164).

Table 8. Results of z-Test: Two Sample Means for Female Drills’ Activity Time with Enrichment

  Eschu Nora
Mean 412 mintues 373 minutes
Variance 448.313 542.171
Observations 33 days 33 days
Hypothesized Mean Difference 0  
z Stat 0.21  
Critical z 1.64 Fail to Reject

Table 8 contains the results of the z-test for the two sample means for the female drill’s activity time with enrichment. The mean for Eschu the non-dominant female is 412. The mean for Nora the dominant female is 373. The hypothesized difference in means is 0. That means that if the z stat is rejected the means will be significantly different. The z stat was 0.21. The critical z was 1.64. The z stat is not larger than the critical z. This means that the null could not be rejected showing that there is not enough evidence to support the claim that dominance has an affect on the amount of time a female drill will spend with enrichment.


Figure 9. Comparison of the Means of the Activity Time that Eschu and Nora Spent with Enrichment

Figure 9 is a visual of a mean comparison between the activity time that Eschu and Nora spent with the enrichment. This shows that the means of Eschu’s time spent with enrichment is larger than the mean of Nora’s time spent with the enrichment.


Table 9. Results of f-Test: Two Sample Means for Female Drill’s Activity Time with Enrichment

  Nora Eschu
Mean 373 mintues 412 minutes
Variance 542.171 448.313
Observations 33 days 33 days
df 32 32
f Stat 1.21  
Critical f 1.74 Fail to Reject

Table 9 contains the results of the f-Test: Two Sample for Variance for the male drill’s positive mating behaviors. The variance for positive mating behaviors on enrichment days is 448.313. The variance for the positive mating behaviors on non-enrichment days is 542.171. The degree of freedom is 32. If the f statistic is rejects the null the variances will be significantly different. The f stat was 1.21. The critical f was 1.74. The f stat is not larger than the critical f. This means that the null could not be rejected showing that Variances are equal.


Figure 10. Comparison of the Variance of the Activity Time that Eschu and Nora Spent with Enrichment


Figure 10 is a visual of a variance comparison between the activity time that Eschu and Nora spent with the enrichment. This shows that the variances of Nora’s time spent with enrichment is slightly larger than the variance of Eschu’s time spent with the enrichment.

 

Conclusion:
Problem 1: Male Drill’s Mating Behaviors
Hypothesis 1: The male drill exhibit more negative mating behaviors on non-enrichment than on enrichment days.
The z-Test: Two Sample for Mean for the male drill’s positive mating behaviors failed to reject the null. This means that there is not enough evidence to support the claim that the male drill, Lyle, will exhibit more negative mating behaviors on non-enrichment days than enrichment days.
The f-Test: Two Sample for Variance for the male drill’s negative mating behaviors was significant enough to reject the null. This means that the variances are significantly different, showing that one of the samples has a much larger variance in the range of data collected. The large difference in the variance shows that the range of the data is one of the two data collection is significantly larger than the other.
Hypothesis 2: The male drill exhibit more positive mating behaviors on non-enrichment days than on enrichment days.
The z-Test: Two Sample for Mean for the male drill’s positive mating behaviors failed to reject the null. This means that there is not enough evidence to support the claim that the male drill, Lyle, will exhibit more positive mating behaviors on enrichment days than non-enrichment days.
The f-Test: Two Sample for Variance for the male drill’s positive mating behaviors was not significant enough to reject the null. This means that the variances are equal, showing that the range of data in both collection are not different than one another.
Problem 2: Female Drill’s Dominance and Activity
Hypothesis: Is the mean of the time the dominant female spend with the enrichment greater than the mean of the time the non-dominant female spends with the enrichment?
The z-Test: Two Sample for Mean for the female drill’s time spent with enrichment failed to reject the null. This means that there is not enough evidence to support the claim that the more dominant female will spend more time with the enrichment than the non-dominant female.
The f-Test: Two Sample for Variance for the male drill’s positive mating behaviors was unable reject the null. This means that the variances are equal, showing that the variance of the range of the data collected are about equal with one another

  

Implications:

The hypotheses in this study failed to reject the null. This shows that there is not enough evidence to show that enrichment has an effect on the mating behaviors of the male drill, and that dominance has an effect of the amount of time a female drill will spend with enrichment. The drills seemed to enjoy and be more active on days they had enrichment items that they could consume. Such enrichment items were the log, the wheat grass, the snow with cinnamon and crickets, and the wild bird seed. The drills also showed a liking of the blue crate that was given because they were able to chew on it.

 

Columbus Zoo & Aquarium School: 2006
 
© 2006 All rights reserved.
   

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